1. Field of the Invention
This invention relates to a safety valve for use in the production of oil and gas. It especially relates to a safety valve set in a tubing string of a well drilled in an offshore or water-covered area. In such situations a safety valve is usually set in a tubing string below the mudline. Then, if the tubing string is broken by any means such as a ship or a barge which may be adrift in a storm, the subsea safety valve will shut off the flow of fluids to the tubing string and prevent a "runaway" well which would otherwise occur.
2. Prior Art
There are many subsurface safety valves which are commercially available, and even many others that have been described in the patents and literature. Some of these valves are operated or controlled from the surface, normally by a long, slender tube which supplies fluid under pressure to hold the valve in an open position. If the control fluid supply should be disrupted, such as by the control line breaking, the valve automatically closes. Another type downhole safety valve is that group which are selfcontained; they usually depend upon a pressure drop to the valve as an actuating medium or force. If the pressure drop through the valve becomes excessive, the valve is forced to a closed position.
In regard to prior art, there are many tools which are run and set in sidewall pockets. Perhaps the most common of these are the gaslift valves such as shown in U.S. Pat. No. 3,375,846, for example. None of these sidewall tools of which we have knowledge are used or can be used as safety valves.